Radio phonograph system



Odi.4 15, 1935. C; M 4SlNNETT l RADIO PHONOGRAPH SYSTEM Filed June 24,1935 Oom@ Patented Oct. 15, 1935 UNITED STATES RADIO PHONOGRAPH SYSTEMchester M. simian, Haaaonfiela, N. J., assignerl to Radio Corporation ofAmerica, a corporation of Delaware Application June 24, 1933, Serial No.677,369 v 8 Claims.

The present invention relates to combination radio-phonograph systemsand has for one object to provide a system of that character having animproved and simplified phono-graph switching arrangement and volumecontrol means.

While the phonograph output circuit may be connected with the signalchannel of the receiver at any suitable point, it is more convenient,ordinarily, to provide the connection with the input circuit of one ofthe electric discharge devices or amplifier tubes of the receivingsystem in or adjacent to the audio frequency amplier, such as the inputcircuit of the second or audio frequency detector tube, for example.

In providing a connection o1 the character re- I'erred to, it hasheretofore been necessary to open the input circuit by switching means.It is, therefore, a further object of the present invention to provide asimplified radio-phonograph input circuit for an electric dischargeamplifier device Which obviates the necessity for opening the input orother associated circuits for switching purposes to effect a change toand from radio operation.

A still further object of the present invention is to provide animproved control circuit for a phonograph pickup device having unitaryswitching and phonograph volume control means. In a present preferredembodiment ofthe invention, the electric pickup device and volumecontrol means are connected in parallel and have related impedancevalues such that the volume control means, in effect, is compensated fordesired tonal effects at different sound levels.

The invention will, however, be better understood from the followingdescription when taken in connection with the accompanying drawing, andits scope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a schematic wiring diagram of aradio-phonograph system embodying the invention; and

Fig. 2 is a curve diagram illustrating certain operating characteristicsof the system shown in Fig. 1.

Referring to Fig. 1, 4 and 5 are electric discharge devices or vacuumtubes in the signal channel 6 of a radio apparatus, to which it isdesired to connect an electric pickup device 'I to provide therewith aradio phonograph combination system. The pickup device is provided withthe usual turntable and record drive means indicated generally at 8.

The electric pickup device is arranged to be connected in circuit withone of the electric discharge devices such as the device 5, which ispreferably associated with or located in the audio frequency amplifiersystem of the radio' apparatus. In the present example, the device 5 isthe second detector of a superheterodyne type `5 of receiver. It isprovided with a tuned intermediate frequency input circuit 9 andreceives radio signals through intermediate circuits and apparatusindicated generally at I0, and in input amplifier device 4, which islocated in the input 10 or radio frequency ampliiier portion of thereceiver.

The ainpliier device 4 is also provided with a tuned signal inputcircuit II which is associated with a suitable signal so-urce such as an15 antenna circuit I2 from which signals are received. An outputtransformer I3 is provided as a coupling means in connection with thesucceeding well known elements of the superheterodyne system, indicatedgenerally at III. 20

The detector device 5 is provided with an intermediate frequency inputtransformer IB between the apparatus Ill and the detector tuned inputcircuit indicated at 9, the secondary of the transformer forming part ofsaid tuned circuit. 25

The amplifier device 4 may be of any suitable type and in the presentexample is of the multiple grid type having a heated cathode I5, acontrol grid I6 connected with the input circuit I I, a screen grid I'I,a suppressor grid I8 connected 30 with the cathode as indicated, and anoutput anode I9 vconnected vwith the transformer I3. Cathode, screengrid, and anode circuits 20, 2I and 22, respectively, are provided inconnection with the corresponding electrodes, and the input 35 orcontrol gridcircuit I I is grounded as indicated at 23.

The detector device 5 is of the same type as the device I and isprovided with similar electrodes as indicated. The input circuit, inthis 40 case the tuned circuit 9, is connected with the control grid I6,and a suitable grid filter is provided by a series resistor 24 and acapacitor 25 connected with the cathode lead indicated at 26. Alsoconnected in the cathode lead and between 45 the cathode and ground is aself bias resistor 2l provided with a suitable bypass capacitor 28.

The detector screen grid lead indicated at 29 and the screen grid lead2| for the amplier device are connected through a supply lead 3U 50 witha usual potential supply source such as the direct current potentialdivider indicated at 3|, to receive suitable operating potentialstherefrom. The polarity of the terminals 32 and 33 is indi-Y catedadjacent thereto. In the presentexample the negative terminal isgrounded, as indicated, and is provided with a supply lead 34, while thepositive plate supply lead is indicated at 35. The supply lead 35 forthe screen grids is suitably bypassed to ground and the negative lead 34by a condenser 36.

The output anode circuit for the device 5 is indicated at 31, and forthe reason that the device is a detector in the present example, it isprovided with a suitable intermediate frequency choke and condenserbypass means 38 and 39, respectively, forming a filter therein.

A suitable output circuit coupling impedance device, such as a resistor40, is provided in the output circuit 31, as a coupling means for thefollowing audio frequency amplifier indicated at 4i. The anode circuit31 is connected through the coupling resistor, to the supply sourcethrough the supply lead 35 as is also the supply lead 22 for the anodecircuit of the device 4.

In the present example, for radio volume control purposes, the cathodelead 2i) of the amplier device 4 is returned to a variable section 42 ofthe potential supply source 3l adjacent to the negative end thereof asindicated, whereby the variable section 4I is connected in the cathodereturn lead and may be adjusted to apply to the device 4 a variable biaspotential to control the gain and therefore the signal volume level ofthe system. To this end, the potential existing in the resistor section42 by reason of current flow therethrough is varied by means of amanually movable contact indicated at 43, connected with the terminal33, whereby it variably short circuits the section 42. Since theremaining portion of the section 42 is in series between the grid andcathode of the amplifier device 4, the potential existing across thatremaining portion will then be applied to the grid of the tube as a biaspotential.

Other suitable bias control means may be employed, although that shownis at present preferred, for the reason that one terminal and thevariable contact of the volume control means comprising the resistorsection 42 and the movable contact 43 is at ground potential, while theremaining terminal to which the cathode return lead is connected issubstantially at ground potential for all radio frequency currents.Accordingly, the volume control means is readily adapted for extensionto remote control points.

In addition to the -manual volume control means, there is provided anadditional volume or gain control means which is arranged to beeffective when the phonograph pickup device 1 is in use. As a simpliedand preferred means for reducing the radio volume or the sensitivity ofthe radio receiving apparatus, a self bias resistor 44 is inserted inthe cathode lead 2B and arranged to be controlled by suitable means forcontrolling the phonograph pickup operation.

The resistor 44 is of such a value that when in circuit with thecathode, a relatively high negative bias is placed on the amplifier tube4 in addition to the bias supplied by the volume control section 42 ofthe fixed potential source 3l. The resistance value of the resistor issuch that the negative bias is, in any case, suicient to suppress orreduce the radio signal amplification so that no radio signals may bereceived through the signal channel of the receiver.

As a preferred means for controlling the additional bias source 44 forsuppressing the radio signals, a switch 45 is connected, through a pairof extension leads 46, in parallel with the resistor 44 and is soconnected with a phonograph volume control device 41 that it is actuatedwhen the volume control device is operated to reduce the phonographoutput signal volume substantially to zero. In the present example, theswitch 45 comprises two contacts 48 connected with the leads 46 andarranged to be shunted by a movable contact 4S which,'in turn, isconnected in any suitable manner vwith the movable element 50 of thephonograph volume control device 41 as indicated.

The volume control device is a simple variable resistor comprising aresistance element 5| along which the movable contact 50 is arranged tobe moved, and is connected in parallel with the pickup device 1 througha pair of leads 52 which preferably are shielded, the shielding beingindicated at 53 and being grounded by a lead 54 to the grounded supplylead 34.

A pair of phonograph pickup output leads 55 are connected in parallelwith the leads 52, and are extended through a grounded shield 56 to theinput or grid circuit of the device 5, although they may be connectedinto the signal channel 6 at any other suitable point. However, thecircuit must be capable of transmitting the audio frequency signalsdelivered by the pickup device and, therefore, the second detector inputcircuit is preferable since it provides an additional ampliiier and isdirectly connected with the audio frequency amplier, in the usual radioreceiving apparatus.

In the present example, the phonograph pickup output leads 55 areconnected with the grid I6 of the detector device 5 between the highfrequency input circuit 9 and the grid lter means 24-25. It will benoted that the phonograph pickup circuit comprises a single pair ofshielded leads which may be extended to remote points of operation forthe phonograph pickup device per se. The two-wire circuit is madepossible by the use of a shunt variable resistor type of volume controldevice as distinguished from the usual potentiometer type requiringthree terminals and three connection leads therefor, as is well known.

This circuit arrangement has the further advantage that, as thephonograph signal volume is reduced by reducing the volume of theresister 5! through movement of the contact 50, the pickup device isgradually short circuited until nally when near the zero volume positioncorresponding to the left hand position as viewed in the drawing, thepickup device is entirely short circuited and entirely removed from thegrid circuit.

Thus as the phonograph volume control device is moved toward the zerovolume position, the series connection for the pickup device with theinput circuit for the tube 5, is gradually short circuited whereby thesignal output from the pickup device and its connection with the gridcircuit are simultaneously controlled by a single device and a volumecontrol operation.

Since the phonograph pickup output leads are connected between the highfrequency input circuit and the high frequency filter means, the biaspotential set up by the self bias resistor 21 for detector operation isnot changed. It has been found that by the proper selection of the valueof the self bias resistor 21, equally satisfactory detector andamplifier action may be obtained without changing the bias, therebysimplifying the change over from radioto phonograph operation.

It has also been found that this shunt volume control means has thefurther advantage that a compensated tone control feature simultaneouswith volume control may be obtained by properly relating the impedanceof the pickup device to that of the shunt volume control resistor.

By way of example, in one embodiment of the invention, a 1500 turnpickup winding is provided which has approximately 1200 ohms resistanceat 1000 cycles and this resistance drops to approximately 100 ohms at100 cycles. The shunt volume control resistor 5l has a maximumresistance of 5000 ohms. Assuming now that the volume setting of thevolume control device 41 is reduced to a relatively low value such aspercent, and with the shunt volume control resistor then having a valueof approximately 1000 ohms, it will be seen that the shunting effect ofthe. volume control resistor across the pickup device and its outputcircuit will be appreciable at 1000 cycles and at higher frequencies,but at 00 cycles and below it may be considered to have substantially arelatively low shunting effect upon the signal potentials delivered bythe pickup device. The low frequency signals will therefore beattenuated much less than the higher frequency signals.

The shunting effect or tone control feature mayfurther be illustrated inconnection with Fig. 2, in which two curves plotted against gain orsignal potential delivered by the pickup, and frequency, are shown at 51and 58, 5l being the response curve of the pickup circuit when thevolume control device is adjusted for 'substantially maximum or highvolume with the entire resistance of 5000 ohms across the pickup deviceoutput circuit, and the curve 58 is the response characteristic of thepickup circuit when the volume is reduced to a relatively low value asabove described.

From an inspection of the curves, it will be seen that upon thelistening ear, the compensation provides an improved effect, in that thesignals in the low audio frequency range are not reduced to the sameextent as are the signals in the higher audio frequency range, it beingknown that at low sound volume levels, the lower frequency signals mustbe materially increased in volume level over the higher mid frequencyrange in order to provide the same sound level effect upon the ear asprovided by a sound output device connected with the system, such as aloud speaker device shown at 59 in connection with the output circuit 60of the audio frequency amplier 4|. In the present example, the loudspeaker device 59 forms the output device of the signal channel of theradio receiver and repre-4 sents any suitable output device for theamplifier system.

From the foregoing description it will be seen that in.accordance withthe invention, a pickup device having a relatively high number of turnsmay be connected directly, without the usual transformer means, with thehigh frequency coupling means in the input or control grid circuit of anelectric discharge device in a signal channel of a radio receiver orlike apparatus. This connection is made, preferably, between the normalinput circuit for said device and the cathode thereof, and preferablywith a grid filter inserted adjacent to the cathode. The device isassociated with or is located in the audio frequency amplifier and may,preferably, be the detector which precedes the audio frequency amplierin the apparatus.

The pickup device is connected, therefore, ln the low potential side ofthe normal control grid input circuit through the medium of a pair ofleads which may be shielded and extended to any remote location for thepickup device.

The simple two-wire pickup device output circuit formed by said leads isshunted by a variable resistor requiring but two leads for yconnectionwith the pickup circuit, and the resistor has, preferably, a maximumresistance greater than the resistance of the pickup device at a certainhigher audio frequency range and which may be reduced to a value lowerthan the resistance of the pickup device .at a certain low audiofrequency range. l

Furthermore, it will be seen that as an independent means separate fromthe normal manual volume control means for the radio receiving channel,an additional gain control means is provided, and is arranged to beactuated simultaneously with and by the phonograph volume control meanswhen the latter is moved to substantially the zero volume controlposition. A

movement of the volume control means to the zero phonograph volumeposition, causing 'the auxiliary gain control means to permit the radioreceiving channel to become operative to receive signals, and a movementofthe phonograph volume control means from said zero position, causingthe auxiliary gain control means to place the radio receiving channelout of operation to receive signals.

As hereinbefore noted, the grid bias of the electric discharge device 5is not changed when the phonograph pickup devic'e is connected incircuit therewith. With this arrangement, furthermore, the pickup deviceis permanently connected with the radio signal channel, and the shuntvariable volume control resistor is the sole means for rendering thepickup device inoperative or effectively disconnected from the radiochannel. The phonograph volume control means further operates in oneposition to control the sensitivity of the radio receiving systemwhereby it is rendered operative or inoperative simultaneously withmovement of the volume control means to and from the substantially zerophonograph volume position.

While the invention has been described in connection with the seconddetector of a superheterodyne receiver, it should be understood that itis not limited in its application tosuch apparatus, but may be appliedto substantially any radio apparatus in connection with the audiofrequency signal channel thereof.

I claim as my invention:

1. In a radio phonograph system, the combination of means for renderingsaid system inoperative to receive radio signals, a detector gridcircuit forming part of the signal channel of said o system, aphonograph pickup device connected permanently in series with said gridcircuit, volume control means comprising a variable resistor connectedin parallel with said pickup device, said resistor being variablebetween a maximum resistance value substantially higher than theresistance of said pickup device and a minimum resistance value, andmeans providing an operating connection between said volume controlmeans and said rst named means for actuating the latter when said volumecontrol means is moved from the substantially zero volume position. l

2. In a radio phonograph system, a phonograph pickup output circuit, aphonograph vol- 1 ume control variable resistor connected in shunttherewith, means for rendering said system inoperative to receive radiosignals, said resistor having a maximum resistance value substantiallygreater than the impedance of the phonograph pickup circuit, and saidiirst named means oomprising a resistor for controlling the radio signalgain in said system and a switch connected in circuit with said resistorand arranged to be actuated by operation of said volume control resistorwhen passing through a predetermined position of adjustment.

3. In a radio receiving system, the combination with a detector having asignal input circuit, of a phonograph pickup device connectedpermanently in series with said input circuit in the low potential sidethereof, a phonograph volume control means connected in parallel withsaid pickup device and being adjustable between a position of maximumimpedance substantially greater than that of the pickup device and aposition of minimum impedance whereat said pickup device issubstantially short circuited, and additional means connected with saidVolume control means for simultaneously rendering said radio receivingsystem operative to receive radio signals when said volume control meansis moved to said last named position.

4. In a radio receiving system, the combination with an electricdischarge detector device having a control grid and a cathode, a signalinput circuit connected with said control grid and an electrical ltermeans connected with the input circuit adjacent to the cathode thereof,of a phonograph pickup device connected permanently in series with saidinput circuit in the low potential side thereof adjacent to said ltermeans, a phonograph volume control means connected in parallel with saidpickup device and being adjustable between a position of maximumimpedance substantially greater than that of the pickup device and aposition of minimum impedance whereat said pickup device issubstantially short circuited, and means for simultaneously renderingsaid radio receiving system operative to receive radio signals when saidvolume control device is moved to said last named position.

5. In a radio receiving system comprising a high frequency amplifier anda detector of the electric discharge type, said detector and ampliiiereach having a control grid, a cathode and an anode, of a phonographpickup device connected permanently in series with the grid circuit ofsaid detector device, a volume control resistor connected in parallelwith Vsaid pickup device, and means for simultaneously varying saidresistor and applying a biasing potential on said amplier grid.

6. l'n a radio receiving system comprising a high frequency ampliiierand a detector of the electric discharge type, said detector and ampliereach having a control grid, a cathode and an anode,rof a phonographpickup device connected permanently in series with the grid circuit ofsaid 'detector device, a volume control resistor connected in parallelwith said pickup device, and means for simultaneously varying saidresistor and controlling the amplifier gain, said last named meanscomprising a movable contact on said resistor, and a switch connectedtherewith to be actuated thereby when moved to substantially the zeroresistance position, said switch being connected with the amplifier tocontrol the application of a biasing potential thereto.

7. In a radio receiving system comprising a high frequency amplifier anda detector of the electric discharge type, said detector and ampliereach having a control grid, a cathode and an anode, of a pair ofphonograph pickup output leads connected permanently with the gridcircuit or said detector device, a volume control resistor connected inparallel with said pickup device, means for simultaneously varying saidresistor and controlling a biasing potential on said amplifier grid,said last named means comprising a movable contact for `said resistorand a switch actuated thereby when moved to substantially the zeroresistance position, a self bias resistor in the cathode lead of saidamplifier, and leads connected between VsaidA switch and said resistorto connect the switch effectively in parallel therewith.

8. In a radio phonograph system, the combination of radio volume controlmeans, phonograph volume control means, means providing a connectionbetween said volume control means whereby the radio volume control meansis actuated to permit radio signals to be received when the phonographvolume control means is adjusted to a zero volume position, a phonographpickup circuit, and an electronic amplier grid circuit, said phonographvolume control means comprising a variable resistor connected in serieswith i said grid circuit and in parallel with said phonograph pickupcircuit.

CHESTER M. SINNETT.

